Here's a video we made to cover a bunch of the basics. Of note, you can now buy 6 members instead of 5 for 3 points each.

I talk about it in the vidieo, but to answer your specific question: There's a maximum amount of XP you can gain in any single match of squads. This prevents people who are awesome at it from farming it for really easy XP. If you're hitting it right near the end of the match, you're not wasting much potential. but if you're constantly getting it mid match, you might want to play regular multiplayer to gain XP faster. (If that's what you're looking for)

That does seem to be the case. Squad mode is a great place to level up oddball members though and boost your squad points easily that way. The bots aren't as tough as real players, so just about any soldier build can gain XP and level up at a decent rate.